/*
尽可能还原 Promise 中的每一个 API, 并通过注释的方式描述思路和原理.
*/

const PENDING = 'pending' // 等待
const FULFILLED = 'fulfilled' // 成功
const REJECTED = 'rejected' // 失败
class MyPromise {
    constructor(executor) {
        try {
            executor(this.resolve, this.reject)
        } catch (error) {
            this.reject(error)
        }
    }
    // promise 状态
    status = PENDING
    // 成功之后的值
    value = undefined
    // 失败原因
    reason = undefined
    // 成功回调
    successCallback = []
    // 失败回调
    failCallback = []

    resolve = (value) => {
        // 如果状态不是等待 阻止状态向下执行
        if (this.status !== PENDING) return;
        // 将状态更改为成功
        this.status = FULFILLED
        // 保存成功之后的值
        this.value = value
        // 判断成功回调是否存在 如果存在 调用
        // this.successCallback && this.successCallback(this.value)
        // 用数组存储多个promise回调函数
        while (this.successCallback.length !== 0) {
            this.successCallback.shift()()
        }
    }

    reject = (reason) => {
        // 如果状态不是等待 阻止状态向下执行
        if (this.status !== PENDING) return;
        // 将状态更改为失败         
        this.status = REJECTED
        // 保存失败之后的值
        this.reason = reason
        // 判断失败回调是否存在 如果存在 调用
        // this.failCallback && this.failCallback(this.reason)
        while (this.failCallback.length !== 0) {
            this.failCallback.shift()()
        }
    }

    then(successCallback, failCallback) {
        successCallback = successCallback ? successCallback : value => value
        failCallback = failCallback ? failCallback : reason => { throw reason }
        let promise2 = new MyPromise((resolve, reject) => {
            // 判断状态
            if (this.status === FULFILLED) {
                // 为了获取promise2，异步执行
                setTimeout(() => {
                    try {
                        let x = successCallback(this.value)
                        // 判断X值是普通值还是promise对象
                        // 如果是普通值 直接调用resolve
                        // 如果是promise对象 查看promise对象返回的结果
                        // 再根据promise对象返回的结果 决定调用resolve 还是调用reject
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (error) {
                        reject(error)
                    }
                }, 0)
            } else if (this.status === REJECTED) {
                setTimeout(() => {
                    try {
                        let x = failCallback(this.reason)
                        resolvePromise(promise2, x, resolve, reject)
                    } catch (error) {
                        reject(error)
                    }
                }, 0)
            } else {
                // 等待
                // 将成功、失败回调存储起来
                this.successCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = successCallback(this.value)
                            resolvePromise(promise2, x, resolve, reject)
                        } catch (error) {
                            reject(error)
                        }
                    }, 0)
                })
                this.failCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = failCallback(this.reason)
                            resolvePromise(promise2, x, resolve, reject)
                        } catch (error) {
                            reject(error)
                        }
                    }, 0)
                })
            }
        })

        return promise2;
    }
    finally(callback) {
        return this.then(val => {
            return MyPromise.resolve(callback()).then(() => val)
        }, (resaon) => {
            return MyPromise.resolve(callback()).then(() => { throw resaon })

        })
    }
    catch(failCallback) {
        return this.then(undefined, failCallback)
    }
    static all(array) {
        let result = [];
        let index = 0;
        return new MyPromise((resolve, reject) => {
            function addData(key, value) {
                result[key] = value
                index++
                if (index === array.length) {
                    resolve(result)
                }
            }
            for (let i = 0; i < array.length; i++) {
                let current = array[i]
                if (current instanceof MyPromise) {
                    // promise对象
                    current.then(value => addData(i, value), reason => reject(reason))
                } else {
                    // 普通值
                    addData(i, current)
                }
            }
        })
    }
    static resolve(value) {
        if (value instanceof MyPromise) return value
        return new MyPromise((resolve) => resolve(value))
    }

}

function resolvePromise(promise2, x, resovle, reject) {
    if (promise2 === x) {
        return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
    }
    if (x instanceof MyPromise) {
        // promise 对象
        // x.then((value) => resovle(value), (reason) => reject(reason))
        x.then(resovle, reject)
    } else {
        // 普通值
        resovle(x)
    }
}

module.exports = MyPromise;